The roofed paper container filled with liquid is formed by preparing a bottomed square cylindrical container formed of a paper packaging material having a thermoplastic resinous layer provided on the outside and inside surfaces; standing the container vertically with the container bottom positioned below and the container opening positioned upper; sterilizing the inside of the container; filling a content liquid as a drink, such as milk, a juice or others through an opening in the top of the container; applying hot blast to the part-to-be-hermetically sealed of the inside of the top of the container to soften/melt the thermoplastic resinous layer; and pressing the part-to-be-hermetically sealed to hermetically seal the top opening. The series of these steps (preparing the container, standing the container, the sterilization, filling a liquid, hermetically-sealing the upper part, etc.) is performed inside the packaging/filling device.
In the above-described packaging/filling, a blank in a square cylindrical developed shape (FIG. 1(A)) is formed into a cylinder with a vertical seal, and then the bottom is folded in to form the bottom by thermal press, and the square cylindrical container is formed (FIG. 1(D)). The roofed paper container (FIG. 1(E)) is formed by the series of the above-described steps.
In the packaging and filling device, a blank of a paper container having the developed shaped and the fold lines as illustrated in FIG. 1(A) is used. The blank has a first bottom panel 1b and a third bottom panel 3b extended from the respective lower sides of a first panel 1 and a third panel 3 which correspond to one pair of 2 opposed container sidewalls; a second bottom panel bottom panel 2b and a fourth bottom panel 4b extended from the respective lower sides of a second panel 2 and a fourth panel 4 which correspond to the other pair of 2 opposed sidewalls; a fifth panel 6 extended from a part of the lower side of the third bottom panel 3b; and plural upper panels it, 2t, 3t, 4t which correspond to the top of the container. In the packaging and filling device, for example, the prior bending mechanism is not used, and the sixth panel is bent with a bending member having 2 curved portions in the step of forming the bottom of the container after the heating step of heating to melt and soften the thermoplastic resinous layer of polyethylene or others on the inside and the outside surfaces (refer to, e.g., Patent Reference 1).
The sixth panel is bent to cover the lower surface of the paper packaging material exposed on the inside surface of the container bottom to thereby protected from permeation leakage.